Optical imaging system

ABSTRACT

An optical imaging system includes a first lens having a positive refractive power, a second lens having a refractive index of 1.65 or greater, a third lens having positive refractive power and a refractive index of 1.65 or greater, a fourth lens having a positive refractive power, a fifth lens having a refractive index of 1.65 or greater, a sixth lens having a refractive index of 1.65 or greater, and a seventh lens having a positive refractive power. The first to seventh lenses are sequentially disposed from an object side to an imaging plane.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit under 35 U.S.C. § 119(a) of KoreanPatent Application No. 10-2016-0179151, filed on Dec. 26, 2016 in theKorean Intellectual Property Office, the entire disclosure of which isincorporated herein by reference for all purposes.

BACKGROUND 1. Field

The following description relates to a telescopic optical imaging systemincluding seven lenses.

2. Description of Related Art

In small cameras, the size of a pixel in an image sensor is reduced whenthe camera's resolution is improved. In detail, image sensors of camerasimplementing a high resolution, of 12 megapixels or greater, may includepixels smaller than that of image sensors of cameras implementing aresolution of 8 megapixels. Because such pixels lead to a reduced amountof light incident on each pixel in the image sensors, the implementationof clear and bright images is difficult. Thus, optical imaging systemscapable of improving the resolution and brightness of small cameras arebeing developed.

SUMMARY

This Summary is provided to introduce a selection of concepts in asimplified form that are further described below in the DetailedDescription. This Summary is not intended to identify key features oressential features of the claimed subject matter, nor is it intended tobe used as an aid in determining the scope of the claimed subjectmatter.

In one general aspect, an optical imaging system includes a first lenshaving a positive refractive power, a second lens a refractive index of1.65 or greater, a third lens having a positive refractive power and arefractive index of 1.65 or greater, a fourth lens having a positiverefractive power, a fifth lens having a refractive index of 1.65 orgreater, a sixth lens having a refractive index of 1.65 or greater, anda seventh lens having a positive refractive power. The first to seventhlenses are sequentially disposed from an object side to an imagingplane.

The first to seventh lenses of the optical imaging system may be formedusing a plastic material. The first lens of the optical imaging systemmay have a convex object-side surface and a concave image-side surfacealong an optical axis. The second lens of the optical imaging system canhave a convex object-side surface and a concave image-side surface alongan optical axis. The third lens of the optical imaging system may have aconvex object-side surface and a concave image-side surface along anoptical axis.

The fourth lens of the optical imaging system can have opposing convexsurfaces along an optical axis. The fifth lens of the optical imagingsystem may have a convex object-side surface and a concave image-sidesurface along an optical axis. The sixth lens of the optical imagingsystem can have a convex object-side surface and a concave image-sidesurface along an optical axis. The seventh lens of the optical imagingsystem may have a convex object-side surface and a concave image-sidesurface along an optical axis.

The optical imaging system may satisfy the expression V2+V3<V1, where V1represents an Abbe number of the first lens, V2 represents an Abbenumber of the second lens, and V3 represents an Abbe number of the thirdlens. The optical imaging system can satisfy the expression V5+V6<V4,where V4 represents an Abbe number of the fourth lens, V5 represents anAbbe number of the fifth lens, and V6 represents an Abbe number of thesixth lens. The optical imaging system may satisfy the expressionCT2<0.2 mm, where CT2 represents a thickness of the second lens. Theoptical imaging system can have an F number that is less than or equalto 2.09.

In another general aspect, an optical imaging system includes a firstlens having a positive refractive power, a second lens having arefractive index greater than or equal to 1.65, a third lens having apositive refractive power and a refractive index greater than or equalto 1.65, a fourth lens having a positive refractive power, a fifth lenshaving a refractive index greater than or equal to 1.65, a sixth lenshaving a refractive index greater than or equal to 1.65, and a seventhlens having a positive refractive power. The first to seventh lenses aresequentially disposed from an object side to an imaging plane.

The sixth lens of the optical imaging system may include an inflectionpoint formed on one or both of an object-side surface or an image-sidesurface. The seventh lens of the optical imaging system can include aninflection point formed on one or both of an object-side surface or animage-side surface.

In another general aspect, an optical imaging system includes a firstlens having a positive refractive power, a second lens having a negativerefractive power, a third lens having a positive refractive power, afourth lens having a positive refractive power, a fifth lens having apositive refractive power, a sixth lens having a negative refractivepower, and a seventh lens having a positive refractive power. The firstto seventh lenses are sequentially disposed from an object side to animaging plane. The second lens, the third lens, the fifth lens, and thesixth lens each have a refractive index greater than or equal to 1.65.An F number of the optical imaging system is less than or equal to 2.09.

The first lens, the second lens, the fourth lens, and the seventh lensof the optical imaging system may each include a convex object-sidesurface along an optical axis. The optical imaging system can satisfythe expression 1.0<TTL/f, where TTL represents a distance from anobject-side surface of the first lens to an imaging plane and frepresents a focal length of the optical imaging system.

Other features and aspects will be apparent from the following detaileddescription, the drawings, and the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram of an optical imaging system according to a firstexample.

FIG. 2 is a set of graphs illustrating aberration curves of the opticalimaging system illustrated in FIG. 1.

FIG. 3 is a table listing aspherical characteristics of the opticalimaging system illustrated in FIG. 1.

FIG. 4 is a diagram of an optical imaging system according to a secondexample.

FIG. 5 is a set of graphs illustrating aberration curves of the opticalimaging system illustrated in FIG. 4.

FIG. 6 is a table listing aspherical characteristics of the opticalimaging system illustrated in FIG. 4.

FIG. 7 is a diagram of an optical imaging system according to a thirdexample.

FIG. 8 is a set of graphs illustrating aberration curves of the opticalimaging system illustrated in FIG. 7.

FIG. 9 is a table listing aspherical characteristics of the opticalimaging system illustrated in FIG. 7.

Throughout the drawings and the detailed description, the same referencenumerals refer to the same elements, where applicable. The drawings maynot be to scale, and the relative size, proportions, and depiction ofelements in the drawings may be exaggerated for clarity, illustration,or convenience.

DETAILED DESCRIPTION

Hereinafter, examples will be described with reference to the attacheddrawings. Examples provide a high-resolution, bright optical imagingsystem capable of being mounted in a small terminal. The disclosure may,however, be exemplified in many different forms and should not beconstrued as being limited to the specific embodiments set forth herein.Rather, these embodiments are provided so that this disclosure will bethorough and complete, and will fully convey the scope of the disclosureafter an understanding of the application.

Throughout the specification, it will be understood that when anelement, such as a layer, region or wafer (substrate), is referred to asbeing “on,” “connected to,” or “coupled to” another element, it can bedirectly “on,” “connected to,” or “coupled to” the other element, orother elements intervening therebetween may be present. In contrast,when an element is referred to as being “directly on,” “directlyconnected to,” or “directly coupled to” another element, there may be noelements or layers intervening therebetween. As used herein, the term“and/or” includes any and all combinations of one or more of theassociated listed items.

Although terms such as “first,” “second,” and “third” may be used hereinto describe various components, regions, or sections, these components,regions, or sections are not to be limited by these terms. Rather, theseterms are only used to distinguish one component, region, or sectionfrom another component, region, or section. Thus, a first component,region, or section referred to in examples described herein may also bereferred to as a second component, region, or section without departingfrom the teachings of the examples.

The articles “a,” “an,” and “the” are intended to include the pluralforms as well, unless the context clearly indicates otherwise. The terms“comprises,” “includes,” and “has” specify the presence of statedfeatures, numbers, operations, members, elements, and/or combinationsthereof, but do not preclude the presence or addition of one or moreother features, numbers, operations, members, elements, and/orcombinations thereof.

Due to manufacturing techniques and/or tolerances, variations of theshapes shown in the drawings may occur. Thus, the examples describedherein are not limited to the specific shapes shown in the drawings, butinclude changes in shape that occur during manufacturing.

The features of the examples described herein may be combined in variousways as will be apparent after an understanding of the disclosure ofthis application. Further, although the examples described herein have avariety of configurations, other configurations are possible as will beapparent after an understanding of the disclosure of this application.

In the present specification, a first lens refers to a lens closest toan object or a subject of which an image is captured. A seventh lensrefers to a lens closest to an imaging plane or an image sensor. In thepresent specification, an entirety of a radius of curvature, athickness, a distance from an object-side surface of a first lens to animaging plane (TTL), a half diagonal length of the imaging plane (IMGHT), and a focal length of a lens is indicated in millimeters (mm). Aperson skilled in the relevant art will appreciate that other units ofmeasurement may be used. Further, in embodiments, all radii ofcurvature, thicknesses, OALs (optical axis distances from the firstsurface of the first lens to the image sensor), a distance on theoptical axis between the stop and the image sensor (SLs), image heights(IMGHs) (image heights), and back focus lengths (BFLs) of the lenses, anoverall focal length of an optical system, and a focal length of eachlens are indicated in millimeters (mm). Likewise, thicknesses of lenses,gaps between the lenses, OALs, TLs, SLs are distances measured based onan optical axis of the lenses.

In a description of a form of a lens, a surface of a lens being convexmeans that an optical axis portion of a corresponding surface is convex,while a surface of a lens being concave means that an optical axisportion of a corresponding surface is concave. Therefore, in aconfiguration in which a surface of a lens is described as being convex,an edge portion of the lens may be concave. In a manner the same as thecase described above, even in a configuration in which a surface of alens is described as being concave, an edge portion of the lens may beconvex. In other words, a paraxial region of a lens may be convex, whilethe remaining portion of the lens outside the paraxial region is eitherconvex, concave, or flat. Further, a paraxial region of a lens may beconcave, while the remaining portion of the lens outside the paraxialregion is either convex, concave, or flat. In addition, in anembodiment, thicknesses and radii of curvatures of lenses are measuredin relation to optical axes of the corresponding lenses.

In accordance with illustrative examples, the embodiments described ofthe optical system include seven lenses with a refractive power.However, the number of lenses in the optical system may vary in someembodiments, for example, between two to seven lenses, while achievingone or more results and benefits described below. Also, although eachlens is described with a particular refractive power, a differentrefractive power for at least one of the lenses may be used to achievethe intended result.

An optical imaging system includes seven lenses. For example, theoptical imaging system may include the first lens, a second lens, athird lens, a fourth lens, a fifth lens, a sixth lens, and the seventhlens, sequentially disposed from an object side to an imaging plane.

The first lens has a refractive power. For example, the first lens has apositive refractive power. The first lens has a convex surface. In anembodiment, the first lens has a convex object-side surface.

The first lens has an aspherical surface. For example, both surfaces ofthe first lens are aspherical. The first lens may be formed using amaterial having a relatively high degree of light transmittance andexcellent workability. In an example, the first lens is formed using aplastic material. The first lens has a relatively low refractive index.In an embodiment, a refractive index of the first lens is less than 1.6.

The second lens has a refractive power. For example, the second lens hasa negative refractive power. The second lens has a convex surface. In anembodiment, the second lens has a convex object-side surface.

The second lens has an aspherical surface. For example, the second lenshas an aspherical object-side surface. The second lens may be formedusing a material having a relatively high degree of light transmittanceand excellent workability. As an example, the second lens may be formedusing a plastic material. The second lens has a refractive index higherthan that of the first lens. In an embodiment, the refractive index ofthe second lens is greater than or equal to 1.6.

The third lens has a refractive power. For example, the third lens has apositive refractive power.

The third lens has an aspherical surface. In an embodiment, the thirdlens has an aspherical image-side surface. The third lens may be formedusing a material having a relatively high degree of light transmittanceand excellent workability. In an example, the third lens is formed usinga plastic material. The third lens may have a refractive indexsubstantially similar to that of the second lens. In an embodiment, therefractive index of the third lens is greater than or equal to 1.6.

The fourth lens has a refractive power. For example, the fourth lens hasa positive refractive power. The fourth lens has a convex surface. In anembodiment, the fourth lens has a convex object-side surface.

The fourth lens has an aspherical surface. For example, both surfaces ofthe fourth lens are aspherical. The fourth lens may be formed using amaterial having a relatively high degree of light transmittance andexcellent workability. In an example, the fourth lens is formed using aplastic material. The fourth lens has a refractive index substantiallythe same as that of the first lens. In an embodiment, the refractiveindex of the fourth lens is less than 1.6.

The fifth lens has a refractive power. For example, the fifth lens has apositive refractive power.

The fifth lens has an aspherical surface. In an embodiment, bothsurfaces of the fifth lens are aspherical. The fifth lens may be formedusing a material having a relatively high degree of light transmittanceand excellent workability. In an example, the fifth lens is formed usinga plastic material. The fifth lens may have a refractive indexsubstantially the same as that of the third lens. For example, therefractive index of the fifth lens is greater than or equal to 1.6.

The sixth lens has a refractive power. For example, the sixth lens has anegative refractive power. The sixth lens may have an inflection point.In an embodiment, the sixth lens includes one or more inflection pointsformed on opposing surfaces.

The sixth lens has an aspherical surface. For example, both surfaces ofthe sixth lens are aspherical. The sixth lens may be formed using amaterial having a relatively high degree of light transmittance andexcellent workability. In an example, the sixth lens is formed using aplastic material. The sixth lens may have a refractive indexsubstantially similar to that of the fifth lens. In an embodiment, therefractive index of the sixth lens is greater than or equal to 1.6.

The seventh lens has a refractive power. For example, the seventh lenshas a positive refractive power. The seventh lens may have a convexsurface. In an embodiment, the seventh lens has a convex object-sidesurface. The seventh lens may have an inflection point. For example, theseventh lens includes one or more inflection points formed on opposingsurfaces.

The seventh lens has an aspherical surface. For example, both surfacesof the seventh lens are aspherical. The seventh lens may be formed usinga material having a relatively high degree of light transmittance andexcellent workability. As an example, the seventh lens is formed using aplastic material. The seventh lens may have a refractive index less thanthat of the sixth lens. In an embodiment, the refractive index of theseventh lens is less than 1.6.

Aspherical surfaces of the first to seventh lenses may be expressedusing Formula 1.

$\begin{matrix}{Z = {\frac{{cr}^{2}}{1 + \sqrt{1 - {( {1 + k} )c^{2}r^{2}}}} + {A\; r^{4}} + {B\; r^{6}} + {C\; r^{8}} + {D\; r^{10}} + {E\; r^{12}} + {F\; r^{14}} + \;{G\; r^{16}} + {H\; r^{18}} + {J\; r^{20}}}} & \lbrack {{Formula}\mspace{14mu} 1} \rbrack\end{matrix}$

In Formula 1, c represents an inverse of a radius of curvature of alens, k represents a conic constant, r represents a distance from acertain point on an aspherical surface of the lens to an optical axis, Ato J represent aspherical constants, and Z (or SAG) represents adistance between the certain point on the aspherical surface of the lensat the distance r and a tangential plane meeting the apex of theaspherical surface of the lens.

The optical imaging system further includes a filter, an image sensor,and a stop. The filter is interposed between the seventh lens and theimage sensor. The filter may block light having a portion of wavelengthsof visible light, in order to generate a clear image. For example, thefilter blocks light of an infrared wavelength.

The image sensor forms an imaging plane. As an example, a surface of theimage sensor forms the imaging plane. The stop is disposed to adjust anamount of light incident on a lens. In an embodiment, the stop isinterposed between the first lens and the second lens.

The optical imaging system satisfies the following ConditionalEquations:F No.≤2.09  [Conditional Equation 1]V2+V3<V1  [Conditional Equation 2]V5+V6<V4  [Conditional Equation 3]CT2<0.2 mm  [Conditional Equation 4]1.0<TTL/f.  [Conditional Equation 5]

In the Conditional Equations, f represents an overall focal length ofthe optical imaging system, V1 represents an Abbe number of the firstlens, V2 represents an Abbe number of the second lens, V3 represents anAbbe number of the third lens, V4 represents an Abbe number of thefourth lens, V5 represents an Abbe number of the fifth lens, V6represents an Abbe number of the sixth lens, TTL represents a distancefrom an object-side surface of the first lens to an imaging plane, andCT2 represents a thickness of the second lens.

Conditional Equations 2 to 4 are provided as parametric relationshipsfor the miniaturization of the optical imaging system. For example, theoptical imaging system satisfying one or more Conditional Equationsamong Conditional Equations 2 to 4 reduces an overall imaging distance(that is, TTL).

Subsequently, an optical imaging system according to various exampleswill be described. First of all, the optical imaging system according toa first example will be described with reference to FIG. 1. An opticalimaging system 100 includes a first lens 110, a second lens 120, a thirdlens 130, a fourth lens 140, a fifth lens 150, a sixth lens 160, and aseventh lens 170.

The first lens 110 has a positive refractive power, a convex object-sidesurface, and a concave image-side surface. The second lens 120 has anegative refractive power, a convex object-side surface, and a concaveimage-side surface. The third lens 130 has a positive refractive power,a convex object-side surface, and a concave image-side surface. Thefourth lens 140 has a positive refractive power and opposing convexsurfaces. The fifth lens 150 has a positive refractive power, a convexobject-side surface, and a concave image-side surface. The sixth lens160 has a negative refractive power, a convex object-side surface, and aconcave image-side surface. In addition, sixth lens 160 includesinflection points formed on opposing surfaces. The seventh lens 170 hasa positive refractive power, a convex object-side surface, and a concaveimage-side surface. In addition, seventh lens 170 includes inflectionpoints formed on opposing surfaces.

Optical imaging system 100 further includes a filter 180, an imagesensor 190, and a stop ST. Filter 180 is interposed between seventh lens170 and image sensor 190, while stop ST is interposed between first lens110 and second lens 120.

Optical imaging system 100 includes a plurality of lenses havingrelatively high refractive indices. For example, second lens 120, thirdlens 130, fifth lens 150, and sixth lens 160 have refractive indicesgreater than or equal to 1.6. In an embodiment, the refractive indicesof second lens 120, third lens 130, fifth lens 150, and sixth lens 160are greater than 1.65 and less than 2.0.

Optical imaging system 100 is configured to implement a bright opticalimaging system. In detail, an F number of optical imaging system 100 is2.09. Optical imaging system 100 has a relatively wide angle of view.For example, an overall angle of view of the optical imaging system 100is 83.3.

Optical imaging system 100 satisfies each of Conditional Equations 2 to5, described above. As examples, in optical imaging system 100, the sum(V2+V3=40.7) of an Abbe number of second lens 120 (V2=20.35) and an Abbenumber of third lens 130 (V3=20.35) is less than an Abbe number of firstlens 110 (V1=56.11). The sum (V5+V6=40.7) of an Abbe number of the fifthlens 150 (V5=20.35) and an Abbe number of the sixth lens 160 (V6=20.35)is less than an Abbe number (V4=56.11) of the fourth lens 140. Inaddition, a thickness of the second lens 120 is 0.13 mm, while animaging distance to focal length ratio (TTL/f) is 1.20.

An optical imaging system having the configuration described above hasaberration characteristics as illustrated by the graphs in FIG. 2. FIG.3 lists aspherical characteristics of the optical imaging systemaccording to the example. Table 1 lists lens characteristics of theoptical imaging system according to the example.

TABLE 1 First Example F No. = 2.090 f = 3.4900 TTL = 4.200 SurfaceRadius of Thickness/ Abbe Focal No. Curvature Distance index Numberlength S1 First lens 1.3902 0.4852 1.547 56.113 3.203 S2 5.9254 0.1433Stop infinity 0 S3 Second lens 4.5499 0.1300 1.668 20.353 −6.733 S42.2360 0.1251 S5 Third lens 4.2504 0.2259 1.668 20.353 41.230 S6 4.91910.1000 S7 Fourth lens 13.0519 0.2000 1.547 56.113 16.898 S8 −31.40710.1680 S9 Fifth lens 10.936 0.2050 1.668 20.353 87.414 S10 13.35470.3604 S11 Sixth lens 13.1415 0.4077 1.668 20.353 −13.203 S12 5.21200.1000 S13 Seventh lens 1.5777 0.7175 1.537 55.656 127.157 S14 1.35860.1819 S15 Filter Infinity 0.1100 1.518 64.197 S16 Infinity 0.5424 S17imaging Infinity −0.0024 plane

An optical imaging system according to a second example will bedescribed with reference to FIG. 4. An optical imaging system 200includes a first lens 210, a second lens 220, a third lens 230, a fourthlens 240, a fifth lens 250, a sixth lens 260, and a seventh lens 270.

The first lens 210 has a positive refractive power, a convex object-sidesurface, and a concave image-side surface. The second lens 220 has anegative refractive power, a convex object-side surface, and a concaveimage-side surface. The third lens 230 has a positive refractive power,a convex object-side surface, and a concave image-side surface. Thefourth lens 240 has a positive refractive power and opposing convexsurfaces. The fifth lens 250 has a positive refractive power, a convexobject-side surface, and a concave image-side surface. The sixth lens260 has a negative refractive power, a convex object-side surface, and aconcave image-side surface. In addition, sixth lens 260 includesinflection points formed on opposing surfaces. The seventh lens 270 hasa positive refractive power, a convex object-side surface, and a concaveimage-side surface. In addition, seventh lens 270 includes inflectionpoints formed on opposing surfaces.

Optical imaging system 200 further includes a filter 280, an imagesensor 290, and a stop ST. Filter 280 is interposed between seventh lens270 and image sensor 290, while stop ST is interposed between first lens210 and second lens 220.

Optical imaging system 200 includes a plurality of lenses havingrelatively high refractive indices. For example, second lens 220, thirdlens 230, fifth lens 250, and sixth lens 260 have refractive indicesgreater than or equal to 1.6. In an embodiment, the refractive indicesof second lens 220, third lens 230, fifth lens 250, and sixth lens 260are greater than 1.65 and less than 2.0.

Optical imaging system 200 is configured to implement a bright opticalimaging system. In detail, an F number of optical imaging system 200 is1.89. Optical imaging system 200 has a relatively wide angle of view.For example, an overall angle of view of the optical imaging system 200is 83.3.

Optical imaging system 200 satisfies each of Conditional Equations 2 to5, described above. For example, in optical imaging system 200, the sum(V2+V3=40.7) of an Abbe number of second lens 220 (V2=20.35) and an Abbenumber of third lens 230 (V3=20.35) is less than an Abbe number(V1=56.11) of first lens 210. The sum (V5+V6=40.7) of an Abbe number offifth lens 250 (V5=20.35) and an Abbe number of sixth lens 260(V6=20.35) is less than an Abbe number of fourth lens 240 (V4=56.11). Inaddition, a thickness of second lens 220 is 0.144 mm, while an imagingdistance to focal length ratio (TTL/f) is 1.225.

An optical imaging system having the configuration described above hasaberration characteristics as illustrated by the graphs in FIG. 5. FIG.6 lists aspherical characteristics of the optical imaging systemaccording to the example. Table 2 lists lens characteristics of theoptical imaging system according to the example.

TABLE 2 Second Example F No. = 1.890 f = 3.3800 TTL = 4.141 SurfaceRadius of Thickness/ Abbe Focal No. Curvature Distance index Numberlength S1 First lens 1.3852 0.4985 1.547 56.113 3.165 S2 6.0739 0.1481Stop infinity 0 S3 Second lens 4.7250 0.1436 1.668 20.353 −6.656 S42.2628 0.1242 S5 Third lens 3.7948 0.2133 1.668 20.353 38.588 S6 4.34970.0918 S7 Fourth lens 10.9431 0.1985 1.547 56.113 17.363 S8 −70.94670.1687 S9 Fifth lens 9.241 0.2218 1.668 20.353 68.063 S10 11.4872 0.3649S11 Sixth lens 12.8242 0.4171 1.668 20.353 −12.887 S12 5.0838 0.0868 S13Seventh lens 1.5712 0.7230 1.537 55.656 125.277 S14 1.3503 0.2087 S15Filter Infinity 0.1100 1.518 64.197 S16 Infinity 0.4205 S17 imagingInfinity 0.0014 plane

An optical imaging system according to a third example will be describedwith reference to FIG. 7. An optical imaging system 300 includes a firstlens 310, a second lens 320, a third lens 330, a fourth lens 340, afifth lens 350, a sixth lens 360, and a seventh lens 370.

The first lens 310 has a positive refractive power, a convex object-sidesurface, and a concave image-side surface. The second lens 320 has anegative refractive power, a convex object-side surface, and a concaveimage-side surface. The third lens 330 has a positive refractive power,a convex object-side surface, and a concave image-side surface. Thefourth lens 340 has a positive refractive power and opposing convexsurfaces. The fifth lens 350 has a positive refractive power, a convexobject-side surface, and a concave image-side surface. The sixth lens360 has a negative refractive power, a convex object-side surface, and aconcave image-side surface. In addition, sixth lens 360 includesinflection points formed on opposing surfaces. The seventh lens 370 hasa positive refractive power, a convex object-side surface, and a concaveimage-side surface. In addition, seventh lens 370 includes inflectionpoints formed on opposing surfaces.

Optical imaging system 300 further includes a filter 380, an imagesensor 390, and a stop ST. Filter 380 is interposed between seventh lens370 and image sensor 390, while stop ST is interposed between first lens310 and second lens 320.

Optical imaging system 300 includes a plurality of lenses havingrelatively high refractive indices. For example, second lens 320, thirdlens 330, fifth lens 350, and sixth lens 360 have refractive indicesgreater than or equal to 1.6. In detail, the refractive indices ofsecond lens 320, third lens 330, fifth lens 350, and sixth lens 360 aregreater than 1.65 and less than 2.0.

Optical imaging system 300 is configured to implement a bright opticalimaging system. In detail, an F number of optical imaging system 300 is1.89. Optical imaging system 300 has a relatively wide angle of view.For example, an overall angle of view of the optical imaging system 300is 85.2.

Optical imaging system 300 satisfies each of Conditional Equations 2 to5, described above. For example, in optical imaging system 300, the sum(V2+V3=40.7) of an Abbe number of second lens 320 (V2=20.35) and an Abbenumber of third lens 330 (V3=20.35) is less than an Abbe number of firstlens 310 (V1=56.11). The sum (V5+V6=40.7) of an Abbe number of fifthlens 350 (V5=20.35) and an Abbe number of sixth lens 360 (V6=20.35) isless than an Abbe number of fourth lens 340 (V4=56.11). In addition, athickness of second lens 320 is 0.158 mm, while an imaging distance tofocal length ratio (TTL/f) is 1.223.

An optical imaging system having the configuration described above hasaberration characteristics, as illustrated by the graphs in FIG. 8. FIG.9 lists aspherical characteristics of the optical imaging systemaccording to the example. Table 3 lists lens characteristics of theoptical imaging system according to the example.

TABLE 3 Third Example F No. = 1.890 f = 3.7200 TTL = 4.551 SurfaceRadius of Thickness/ Abbe Focal No. Curvature Distance index Numberlength S1 First lens 1.5238 0.5483 1.547 56.113 3.481 S2 6.6813 0.1629Stop infinity 0 S3 Second lens 5.1975 0.1579 1.668 20.353 −7.322 S42.4891 0.1366 S5 Third lens 4.1742 0.2347 1.668 20.353 42.448 S6 4.78460.1010 S7 Fourth lens 12.0374 0.2184 1.547 56.113 19.099 S8 −78.04140.1856 S9 Fifth lens 10.165 0.2440 1.668 20.353 74.869 S10 12.63590.4014 S11 Sixth lens 14.1066 0.4588 1.668 20.353 −14.176 S12 5.59220.0955 S13 Seventh lens 1.7283 0.7953 1.537 55.656 137.796 S14 1.48530.2087 S15 Filter Infinity 0.1100 1.518 64.197 S16 Infinity 0.4907 S17imaging Infinity 0.0014 plane

As set forth above, according to examples, an optical imaging systemcapable of capturing a distant image and being mounted in a smallterminal may be provided. While this disclosure includes specificexamples, it will be apparent after an understanding of this disclosurethat various changes in form and details may be made in these exampleswithout departing from the spirit and scope of the claims and theirequivalents. The examples described herein are to be considered in adescriptive sense only, and not for purposes of limitation. Descriptionsof features or aspects in each example are to be considered as beingapplicable to similar features or aspects in other examples.

Suitable results may be achieved if the described techniques areperformed in a different order, and/or if components in a describedsystem, architecture, device, or circuit are combined in a differentmanner, and/or replaced or supplemented by other components or theirequivalents. Therefore, the scope of the disclosure is defined not bythe detailed description, but by the claims and their equivalents, andall variations within the scope of the claims and their equivalents areto be construed as being included in the disclosure.

What is claimed is:
 1. An optical imaging system, comprising: a firstlens, a second lens, a third lens, a fourth lens, a fifth lens, a sixthlens, and a seventh lens, wherein the first to seventh lenses aresequentially disposed from an object side to an imaging plane, whereinfour or more lenses among the first to seventh lenses have a refractiveindex greater than 1.6, and wherein the fifth lens has a concaveimage-side surface along an optical axis.
 2. The optical imaging systemof claim 1, wherein the first to seventh lenses are formed using aplastic material.
 3. The optical imaging system of claim 1, wherein thefirst lens has a convex object-side surface and a concave image-sidesurface along an optical axis.
 4. The optical imaging system of claim 1,wherein the second lens has a convex object-side surface and a concaveimage-side surface along an optical axis.
 5. The optical imaging systemof claim 1, wherein the third lens has a convex object-side surface anda concave image-side surface along an optical axis.
 6. The opticalimaging system of claim 1, wherein the fourth lens has opposing convexsurfaces along an optical axis.
 7. The optical imaging system of claim1, wherein the fifth lens has a convex object-side surface.
 8. Theoptical imaging system of claim 1, wherein the sixth lens has a convexobject-side surface and a concave image-side surface along an opticalaxis.
 9. The optical imaging system of claim 1, wherein the seventh lenshas a convex object-side surface and a concave image-side surface alongan optical axis.
 10. The optical imaging system of claim 1, wherein theoptical imaging system satisfies the following expression:V2+V3<V1, where V1 represents an Abbe number of the first lens, V2represents an Abbe number of the second lens, and V3 represents an Abbenumber of the third lens.
 11. The optical imaging system of claim 1,wherein the optical imaging system satisfies the following expression:V5+V6<V4, where V4 represents an Abbe number of the fourth lens, V5represents an Abbe number of the fifth lens, and V6 represents an Abbenumber of the sixth lens.
 12. The optical imaging system of claim 1,wherein the optical imaging system satisfies the following expression:CT2<0.2 mm, where CT2 represents a thickness of the second lens.
 13. Theoptical imaging system of claim 1, wherein an F number is less than orequal to 2.09.
 14. An optical imaging system, comprising: a first lenshaving a positive refractive power; a second lens having a refractiveindex greater than or equal to 1.65; a third lens having a positiverefractive power and a refractive index greater than or equal to 1.65; afourth lens having a positive refractive power; a fifth lens having arefractive index greater than or equal to 1.65; a sixth lens having arefractive index greater than or equal to 1.65; and a seventh lenshaving a positive refractive power, wherein the first to seventh lensesare sequentially disposed from an object side to an imaging plane. 15.The optical imaging system of claim 14, wherein the sixth lens includesan inflection point formed on one or both of an object-side surface oran image-side surface.
 16. The optical imaging system of claim 14,wherein the seventh lens includes an inflection point formed on one orboth of an object-side surface or an image-side surface.
 17. An opticalimaging system, comprising: a first lens having a positive refractivepower; a second lens having a negative refractive power; a third lenshaving a positive refractive power; a fourth lens having a positiverefractive power; a fifth lens having a positive refractive power; asixth lens having a negative refractive power; and a seventh lens havinga positive refractive power, wherein the first to seventh lenses aresequentially disposed from an object side to an imaging plane, whereinthe second lens, the third lens, the fifth lens, and the sixth lens eachhave a refractive index greater than or equal to 1.65, and wherein an Fnumber is less than or equal to 2.09.
 18. The optical imaging system ofclaim 17, wherein the first lens, the second lens, the fourth lens, andthe seventh lens each include a convex object-side surface along anoptical axis.
 19. The optical imaging system of claim 17, wherein theoptical imaging system satisfies the following expression:1.0<TTL/f, where TTL represents a distance from an object-side surfaceof the first lens to an imaging plane and f represents a focal length ofthe optical imaging system.